Hydroxy lanthanide ions

The ratio of the size of the metal ion and the radius of the internal cavity of the macrocyclic polyether determines the stoichiometry of these complexes. The stoichiometry of these complexes also depends on the coordinating ability of the anion associated with the lanthanide. For example, 12-crown-4 ether forms a bis complex with lanthanide perchlorate in acetonitrile while a 1 1 complex is formed when lanthanide nitrate is used in the synthesis [66]. Unusual stoichiometries of M L are observed when L = 12 crown-4 ether and M is lanthanide trifluoroacetate [67]. In the case of 18-crown-6 ligand and neodymium nitrate a 4 3 stoichiometry has been observed for M L. The composition of the complex [68] has been found to be two units of [Nd(18-crown-6)(N03)]2+ and [Nd(NCh)<--)]3. A similar situation is encountered [69] when L = 2.2.2 cryptand and one has [Eu(N03)5-H20]2- anions and [Eu(2.2.2)N03]+ cations. It is important to note that traces of moisture can lead to polynuclear macrocyclic complexes containing hydroxy lanthanide ions. Thus it is imperative that the synthesis of macrocyclic complexes be performed under anhydrous conditions. 

The L1 complexes of the middle lanthanides Gd(III), Eu(III), and Tb(III) decompose less rapidly at pH 7.4, 37 °C than do the L1 complexes of La(III) or Lu(III) (14). The fit of the lanthanide ion into the macrocycle may be important here. Certainly, the macrocycle fit will vary for La3+ (116 pM) compared to Lu3+ (97.7 pM) (41). A recent study using luminescence measurements suggests a greater lability of the Eu(L1)3+ complex than previously reported (28). Detection of the Eu(DPTA)-complex produced upon addition of diethylenetriaminepentaacetic acid (DTPA) to Eu(L1)3+ indicates that the complex decomposes approximately 12% in 48 h at 37 °C, pH 7.4. It is noteworthy that solutions of Eu(L1)3+ contain two different species (28). One of them, possibly a hydroxy-bridged dimer, is present in greater amounts at high concentrations of Eu(L1)3+. 

Diene (14) reacted with a series of aldehydes under BFs-OEtz catalysis in CH2CI2 to give predominantly trans products (Table lO). " Aldol-type products, such as p-hydroxy enones, are isolated (along with dihydropyrones) from the reaction mixtures. Using TFA as a catalyst, the p-hydroxy enones are, as previously described, converted into dihydropyrones. The stereoselectivity of these reactions is consistent with a Mukaiyama-aldol reaction rather than a Diels-Aider cycloaddition. The stereochemistry of the P-hydroxy enones is also consistent with the observation that the (Z)-alkoxysilane reacts with the aldehyde in an extended transition state to give anti (threo) aldol products (Scheme 16). In the cases using ZnCh or lanthanide ions as catalysts aldol products have not been detected. 

Based on earlier research on the separation of the lanthanides, ion exchange separations were also done using citric add as a complexant. Because the citrate eluent is plagued by relatively slow kinetics, other hydroxy-carboxylic adds were tested as elutriants for the higher actinide elements. Lactic add was among the first spedes tried, but better interactinide separations were observed using a-hydroxyisobutyric acid... 

Carboxylic and hydroxy carboxylic acids form complexes readily with lanthanides with high stability constants (Chapter 3) and they have been widely used in the ion exchange... 

Complex formation is useful for metal speciation and also for the separation of diverse metal ions. Among a variety of complexing reagents [20-22] cyanide is probably the most important. IPC separation of metal ions as metallocyanide complexes with a suitable cationic IPR is a reliable technique [23]. Complexation of trace level lanthanides with a-hydroxy isobutyric acid and separation under IPC condition shortened analysis time from days to minutes [24]. Flow injection was successfully coupled to IPC to simplify batch precomplexation detection limits were at sub-microgram per liter levels [2]. 

FIG. 16.7. Elution curves for 3+ lanthanide and actinide ions from Dowex-50 ion exchange resin with ammonium-a-hydroxy isobutyrate eluant. (From Katz and Seaborg.)... 

After irradiation the sample was dissolved in hydrochloric acid. A known amount of all the lanthanides (0.5-1 mg. each) and 10 mg. of barium were added, the cerium was oxidized and subsequently reduced to ensure complete exchange of carrier and cerium activity, and the lanthanides were separated and purified as a group using a series of fiuoride and hydroxide precipitations. The final hydroxide precipitate was dissolved in dilute hydrochloric acid and adsorbed to 80 mg. of Dowex 50. The resin was transferred to the top of an ion exchange column (Dowex 50X12, NH4 -form, settling rate 0.5-1.5 cm./min.), and the lanthanides were eluted using a-hydroxy-isobutyric acid and continu-... 

Complexes of lactic acid with a wide variety of metal ions are known and their stability constants have been determined. A variety of techniques has been used in the study of the species formed in the solutions of this hydroxy acid and inorganic ions. Electrochemical and spectrophoto-metric methods have been used with the main aim of determining stability constants of the complex ions. CD and optical rotatory dispersion (ORD) have also proved to be powerful methods in studying, for instance, Mo, Mo , Cu" and Co", as well as lanthanide complexes. Very recently, Brittain et used circularly polarized luminescence (CPL) techniques in the study... 

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